My invention comprises improvements in a planetary multiple-ratio transmission of the kind shown, for example, in my U.S. Pat. No. 4,978,328, issued Dec. 18, 1990, which is assigned to the assignee of my present invention.
The transmission described in that patent includes a hydrokinetic torque converter located on the axis of the crankshaft of an internal combustion engine. An output shaft is arranged in spaced parallel disposition with respect to the engine crankshaft axis. A plurality of simple planetary gear units is disposed on the output shaft axis, the torque output element of the planetary gear units being connected drivably to a final drive which, in turn, distributes torque to the input element of a geared differential.
The output shaft is connected to one output side gear of the differential and extends through the planetary gearing. It is adapted to be connected to a vehicle traction wheel through a universal coupling. A second traction wheel is connected to a companion output shaft connected to a second output side gear of the differential.
Torque is distributed from a turbine member of the hydrokinetic torque converter through a torque transfer drive to the input elements of the planetary gearing.
Friction clutches and brakes are used to establish reaction points in the planetary gearing and to connect one element of the gearing to a companion element as the planetary gearing is conditioned for multiple forward driving ratios and a reverse ratio. A low-speed ratio is achieved by connecting a turbine-driven torque input shaft to a torque input element of the gearing through a friction clutch and an overrunning coupling acting in series relationship in the torque flow path.
The reaction element during low-speed ratio operation is a friction brake. The friction brake used for low-speed ratio operation remains applied during a ratio change to the second ratio as a second friction clutch is applied. The overrunning coupling associated with the first ratio then freewheels.
During direct-drive operation, a second, direct-drive friction clutch is applied as the first friction clutch remains applied, thus connecting the elements of the gearing together for rotation in unison. The direct-drive friction clutch is arranged in series relationship in the torque flow path that distributes torque to one of the input elements of the gearing.
Overdrive operation requires the application of another friction brake, and reverse drive operation requires engagement of a third friction brake.